Synchronous electric machine

Abstract

An electric machine (M) comprises a field (A) and an armature (B) between which is defined an air gap (G). The field (A) has at least one pair of poles (N, S) and the armature (B) has n teeth ( 20 ) and n slots ( 21 ) per pair of poles (N, S) of the field (A). The surface of the field (A) facing the air gap (G) is divided into 2n elements or samples ( 1–12 ) having the same extent along the direction of relative displacement between armature and field, and having a respective magnetic potential value (τ i ). Each sample ( 1–12 ) of the field (A) has a respective total permeance value (pi) at the air gap (G) in a predetermined relative position between armature (B) and field (A). The field (A) comprises a plurality of magnetically distinct ferromagnetic bodies ( 30, 31, 32, . . . ) each of which couples at least two samples of the field in such a way as to ensure a substantial magnetic equipotentiality.

1. A synchronous electric machine (M) comprising an armature (A) and an inductor (B), between which is defined an air gap (G);
 the armature (A) having at least one pair of poles (N, S), 
 the inductor (B) having, for each pair of poles (N, S) of the armature (A), n teeth ( 20 ) and n slots ( 21 ) alternating with one another and having at the air gap (G) respective essentially constant extent in the direction of relative displacement between the inductor (B) and the armature (A); the inductor (B) being provided with a winding (W); 
 the surface of the armature (A) facing the air gap (G) being divided into 2n elements or samples ( 1 – 12 ) for each pair of poles of the armature having substantially the same extent in the said direction of relative displacement; each sample ( 1 – 12 ) having a respective value of magnetic potential (τ 1 ); 
 each sample ( 1 – 12 ) of the armature (A) being associated with a respective value of total magnetic permeance (pi) at the air gap (G) in a predetermined alignment condition or relative position between the inductor (B) and the armature (A) in which the sample extends between the centre line of the opening ( 21   a ) of one slot ( 21 ) and the centre line of the end or pole shoe ( 20   a ) of a tooth at the air gap (G); the value of the total magnetic permeance (pI) associated with at least two samples being different from the value of the total magnetic permeance associated with the other samples; 
 the armature (A) comprising a plurality of bodies ( 30 ,  31 ,  32 ; . . . ) of magnetically distinct ferromagnetic material, each of which couples at least two armature samples in such a way as to ensure a substantial magnetic equipotentiality thereof; 
 the magnetic potentials (τ i ) of the individual samples ( 1 – 12 ) of the armature (A) and the said values of total magnetic permeance (p i ) associated with them being determined according to predetermined criteria; 
 characterized in that the value of magnetic potential (τ i ) of each sample ( 1 – 12 ) is essentailly constant over the extent of the sample in that the inductor (B) is formed in such a way that it is able to generate a magnetomotive force distribution which is seen by the armature (A) identically in all the relative positions spaced from one another by one slot pitch (P), and 
 in that, having defined a first and a second alignment conditions for each sample ( 1 – 12 ), in the first of which the sample ( 1 – 12 ) extends in a given directional sense from the centre line of the opening ( 21   a ) of one slot ( 21 ) to the air gap (G) and the centre line of the end ( 20   a ) of one tooth ( 20 ) at the air gap (G), and in the second of which the sample extends from the centre line of the end ( 20   a ) of one tooth ( 20 ) at the air gap (G) to the centre line of the opening ( 21   a ) of a slot ( 20 ) to the air gap (G), the values of all the magnetic parameters (L o , L m , L om , ψ o , ψ m ) of the electric machine calculated in the components along two separate axes ( o , m), for example at right angles to one another, related to the armature, are substantially equal to one another in the said two alignment conditions. 
 
   
   
     2. An electric machine according to  claim 1 , in which, the samples ( 1 – 12 ) of the armature being assigned respective even and odd positions alternately on the surface facing the air gap (G) along the said direction of relative displacement, for each body ( 31 ,  32 ; . . . ;  101 ,  102 ) of the armature (A) having magnetic potential (τ) substantially different from zero the sum of the total magnetic permeances (p x ) of the samples of even position is substantially equal to the sum of the integral magnetic permeances (p y ) of the samples in odd positions. 
   
   
     3. An electric machine according to  claim 1 , in which the armature (A) comprises at least one ferromagnetic body, defined “odd” ( 30 ;  40 ;  51 ; . . . ;  101 ), which faces the air gap (G) through two non-contiguous sets of samples, each of which comprises an odd number of contiguous samples ( 1 ). 
   
   
     4. An electric machine according to  claim 3 , in which the armature (A), starting from the central body ( 50 ), comprises three contiguous “odd” bodies or layers ( 51 – 53 ) for each pole. 
   
   
     5. An electric machine according to  claim 3 , in which the armature (A) comprises for each pole a single odd body ( 71 ), contiguous with the central body ( 70 ) and which faces the air gap (G) with a single sample ( 2 ) at each of its ends, and a single further body ( 72 ). 
   
   
     6. An electric machine according to  claim 5 , in which the surface of the armature (A) facing the air gap (G) is divided into four groups of six samples ( 1 – 6 ) and, being p 1 , p 2 , . . . , p 6  the values of the magnetic permeance associated with the samples ( 1 – 6 ) of each group starting from the pole separation axis ( o ) of the armature poles, one has that
     p   1   <p   2   ; p   3   <p   4   <p   5 ; and  p   6 <max ( p   2   , p   5 ). 
 
   
   
     7. An electric machine according to  claim 3 , in which the armature (A), in each pole starting from the central body ( 80 ), comprises a first odd body ( 81 ) which faces the air gap (G) with a single sample ( 2 ) at each of its ends, and a second odd body ( 82 ) which is contiguous with the first ( 81 ) and which faces the air gap (G) with three samples ( 3 ,  4 ,  5 ) at each of its ends. 
   
   
     8. An electric machine according to  claim 3 , in which the armature (A) comprises for each pole a single odd body ( 81 ) contiguous with the central body ( 80 ) and which faces the air gap (G) with a single sample ( 2 ) at each of its ends, and two further bodies ( 82 ,  83 ) neither of which is odd. 
   
   
     9. An electric machine according to  claim 3 , in which n=12 and the armature (A) comprises a central body ( 100 ) of ferromagnetic material of zero magnetic potential, the opposite ends of which each form four samples ( 1 ,  2 ,  11 ,  12 ), and four further bodies or layers ( 101 ,  102 ) in pairs of identical bodies or layers; between the bodies ( 100 – 102 ) of the armature (A) there being defined four spaces ( 103 ,  104 ) in which are located respective permanent magnets ( 105 ,  106 ) magnetised orthogonally of the pole separation axis ( o ) of the armature poles (A). 
   
   
     10. An electric machine according to  claim 9 , in which the outermost bodies or layers ( 102 ) of the armature (A) each comprise six contiguous samples ( 4 – 9 ). 
   
   
     11. An electric machine according to  claim 9 , in which the intermediate bodies ( 101 ) of the armature (A) comprise three samples ( 3 – 5 ) at one end, and one sample ( 10 ) at the other end; the outermost bodies or layers ( 102 ) then each comprising four contiguous samples ( 6 – 9 ). 
   
   
     12. An electric machine according to  claim 1 , in which:
   L o,1 ≅L o,2   
   L m,1 ≅L m,2   
   L om,1 ≅L om,2   
   Ψ o,1 ≅Ψ o,2   
   Ψ m,1 ≅Ψ m,2   
 
     where
 L o,1  and L o,2  are the values of self-inductance measured in the said two alignment conditions along a first axis ( o ) corresponding to the pole separation axis (N, S) of the armature (A); 
 L m,1  and L m,2  are the values of self-inductance measured, in the said two alignment conditions, along a second axis (m) at right angles to the separation axis ( o ) of the pole (N, S) of the inductor (A); 
 L om,1  and L om,2  are the values of mutual coupling between magnetomotive forces and fluxes along the said first and second axis ( o , m) in the said two alignment conditions; 
 Ψ o,1  and Ψ o,2  are the values of the flux linked by the windings (W) of the inductor (B) along the said first axis ( o ) in the said two alignment conditions; and
 Ψ m,i ≅Ψ m,2  are the values of the flux linked by the windings (W) of the inductor (B) along the said second axis (m) in the said two alignment conditions. 
 
 
   
   
     13. An electric machine according to  claim 1 , in which the slots ( 21 ) of the inductor (B) have an opening in the surface facing the air gap (G) which, along the said direction of relative displacement, has a width close to ¼ or ⅛ of the slot pitch (P). 
   
   
     14. An electric machine according to  claim 1 , in which the armature (A) comprises at least two axial armature portions which are offset from one another in the said direction of relative displacement. 
   
   
     15. An electric machine according to  claim 14 , in which the said at least two portions of the armature (A) have respective different transverse sections. 
   
   
     16. An electric machine according to  claim 15 , in which the said at least two portions of the armature (A) have respective different axial lengths. 
   
   
     17. A machine according to  claim 14 , in which two portions of the armature (A) are offset from one another by about one quarter of the pitch (P) of the slots ( 21 ) of the inductor (B). 
   
   
     18. An electric machine according to  claim 14 , in which the armature (A) comprises four axial armature portions which, in the said direction of relative displacement are offset from one another by about ⅛ of the slot pitch. 
   
   
     19. An electric machine according to  claim 1 , dimensioned to deliver in operation a maximum predetermined torque (T M ), and in which a first and a second alignment condition is defined for each sample ( 1 – 12 ) of the armature (A) in which the sample extends in a given directional sense from the centre line of the opening ( 21   a ) of one slot ( 21 ) to the air gap to the centre line of the end ( 20   a ) of one tooth ( 20 ) at the air gap and, respectively, from the centre line of the end ( 20   a ) of one tooth ( 20 ) at the air gap to the centre line of the opening ( 21   a ) of a slot ( 21 ) at the air gap, the armature (A) is formed in such a way that when the machine (M) operates delivering a torque close to the said maximum torque (T M ), in each of the said alignment conditions the distribution of induction in the teeth ( 20 ) of the inductor (B) has values substantially close to and preferably less than the value of saturation induction of the teeth ( 20 ) of the inductor (B) on at least half of the pole pitch of the armature (A), and preferably not more than ¾ of the pole pitch of the inductor (A). 
   
   
     20. A synchronous electric machine according to  claim 19 , in which, in each of the said alignment conditions, the said distribution of induction is substantially in quadrature with the distribution of the magnetic potential generated by the inductor (B) at the pole shoes ( 20   a ) of the teeth ( 20 ) of the inductor (B). 
   
   
     21. A synchronous electric machine according to  claim 19 , in which, in each of the said alignment conditions, the said flux distribution has a variation increasing substantially monotonically over about one pole pitch of the armature (A), and decreasing substantially monotonically for the subsequent or preceding pole pitch. 
   
   
     22. An electric machine according to  claim 19 , in which each pole of the armature (A), starting from the central body ( 50 ), has permanent magnets ( 60 ,  62 ,  63 ) interposed between all the contiguous bodies except that between the first and the second odd body ( 51 ,  52 ) the said magnets being magnetised in the same sense in each pole, along the axis (m) of symmetry of the poles. 
   
   
     23. An electric machine according to  claim 19 , in which in each pole of the armature (A), starting from the central body ( 50 ), are interposed permanent magnets ( 60 ,  62 ) between the central body ( 50 ) and the first odd body ( 51 ), and between the second and the third odd body ( 52 ,  53 ); the said permanent magnets being magnetised in the same sense in each pole along the axis (m) of symmetry of the poles. 
   
   
     24. An electric machine according to  claim 1 , in which each pole (N, S) of the armature (A) is specularly symmetric with respect to an axis (m) orthogonal to the said direction of relative displacement, and in which the distribution of the values (pi) of magnetic permeance at the air gap (G) associated with the armature samples has a local minimum at the or each pole separation axis ( o ) of the armature poles (N, S), that is the values (pi) of the magnetic permeance at the air gap (G) increase along the air gap (G) in both directions starting from the or each pole separation axis ( o ) of the armature poles; this magnetic permeance (pi) has its absolute maximum value in correspondence with armature samples lying between the said or each said pole separation axis ( o ) of the armature poles and the adjacent axis of symmetry (m) of the armature poles. 
   
   
     25. An electric machine according to  claim 24 , in which n=3 and the armature (A) comprises three bodies ( 30 – 32 ) of ferromagnetic material separated by spaces ( 33 ,  34 ) in which are disposed permanent magnets ( 35 ,  36 ) magnetised parallel to the axis (m) of symmetry of the poles of the armature (A); the armature (A) comprising a central body ( 30 ) which at its opposite ends forms two armature samples ( 1 — 1 ) and which has magnetic potential (τ 1 ) equal to zero, the magnetic permeance (p 1 ) associated with the samples ( 1 — 1 ) formed by the said central body ( 30 ) being less than that (p 2 , p 3 ) associated with the samples ( 2 – 3 ) formed by the other body ( 31 – 32 ), of the armature (A), the permeances (p 1 , p 3 ) of which are substantially equal to one another. 
   
   
     26. An electric machine according to  claim 24 , in which n=6 and the armature (A) comprises six essentially chordal bodies or layers ( 40 – 42 ) of ferromagnetic material in pairs of bodies equal to one another separated by spaces ( 43 – 45 ) in which are disposed permanent magnets ( 46 – 48 ) magnetised parallel to the axis (m) of symmetry of the poles of the armature (A); the surface of the armature (A) facing the air gap (G) being divided into four groups of three samples ( 1 – 3 ), the samples ( 1 – 3 ) in each group having respective values of magnetic permeance (p 1 , p 2 , p 3 ) at the air gap increasing with the distance from the pole separation axis ( o ) of the armature poles. 
   
   
     27. A machine according to  claim 26 , in which the said magnetic permeances p 1 , p 2  and p 3  at the air gap of the samples ( 1 – 3 ) of each group are substantially such that. 
         0.76   <       p   1       p   2       <     1   ⁢           ⁢   0.8     <       p   2       p   3       <       1   ⁢           ⁢   and   ⁢             ⁢             ⁢     p   1       +     p   3         =     2   ⁢       p   2     .           
 
   
   
     28. An electric machine according to  claim 24 , in which n=12 and in which being p 1  and p 2  the values of the magnetic permeances at the air gap associated with the first two samples ( 1 ,  2 ) of the armature (A) starting from the axis ( o ) of separation of the poles (N, S) of the armature itself, in both directional senses of relative displacement between inductor (B) and armature (A) are related by: 0.93<p 1 /p 2 <1. 
   
   
     29. An electric machine according to  claim 28 , in which the value p 3  of the said magnetic permeance associated with the third samples of the armature (A) starting from the axis ( o ) of separation of the inductor poles, in both said directional senses is such that substantially 
       0.86   <       p   2       p   3       <   1.       
 
   
   
     30. An electric machine according to  claim 28 , in which the armature (A) comprises a central body ( 50 ;  70 ;  80 ) of ferromagnetic material of zero magnetic potential (τ) which has at each end two samples ( 1 — 1 ) contiguous to the or each axis ( o ) of separation of the armature poles. 
   
   
     31. An electric machine according to  claim 28 , in which in the said direction of relative displacement the slots ( 21 ,  21   a ) of the inductor (B) have predetermined periodic widths (b′, b″) different from one another, whilst the teeth ( 20 ) have a substantially constant extent; in each slot ( 21 ) of the inductor (B) there being located a number of conductors substantially proportional to its width (b′; b″). 
   
   
     32. An electric machine according to  claim 31 , in which the said predetermined width (b′, b″) of the slots ( 21 ) have substantially the ratio 2:√{square root over (3)} one another. 
   
   
     33. An electric machine according to  claim 24 , in which n=12 and the armature (A) comprises twelve bodies on layers in equal pairs, separated by eleven spaces in which are disposed respective permanent magnets magnetised parallel to the axis (m) of symmetry of the armature poles (A). 
   
   
     34. A machine according to  claim 1 , in which the armature (A) has asymmetric poles and a central ferromagnetic body of substantially zero magnetic potential which at each of its ends faces the air gap with a plurality of contiguous samples over an overall extent not greater than ⅓ of the armature pole pitch, and in which the total magnetic permeances (pi) associated with the samples of the central ferromagnetic body of the armature (A) have values varying monotonically in dependence on the position co-ordinate along a direction of relative displacement between the inductor (B) and the armature (A). 
   
   
     35. An electric machine according to  claim 34 , in which n=6 and the armature (A) comprises a central body ( 90 ) which at ech of its opposite ends forms two samples ( 1 – 6 ), and a further four bodies or layers ( 91 ,  92 ) in pairs of identical bodies or layers, which at each of their opposite ends form a sample ( 2 ,  5 ;  3 ,  4 ); the samples ( 2 ,  5 ;  3 ,  4 ) formed by each further body ( 91 ,  92 ) being associated with equal values (p 2 =p 5 ; p 3 =p 4 ) of the magnetic permeance at the air gap; between the bodies or layers ( 90 – 92 ) of the armature (A) there being defined four spaces ( 93   a ,  93   b ) in which are located respective permanent magnets ( 94 ,  95 ) magnetised orthogonally of the axis ( o ) of separation of the armature poles.